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	<title>Document</title>
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		table,tr,td {border: 1px solid silver;}
		td { width: 50px;
		     height: 50px;
		     line-height: 50px;
		     text-align: center;
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		td:empty {
		background-color: greenyellow; }
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	     <tr><td>2</td><td>4</td><td>8</td></tr>
	     <tr><td>16</td><td>32</td><td>64</td></tr>
	     <tr><td>128</td><td>256</td><td></td></tr>
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